Thermoplastic skin sheet for interior parts of automobiles and method for producing such skin sheet

Abstract

A thermoplastic skin sheet constituted by (a) a thermoplastic polyolefin or elastomer sheet; (b) a primer layer coated on the sheet, the primer being based on a modified polyolefin resin containing 2 mg-equivalent / g or less of a hydroxyl group or a carboxyl group; and (c) a topcoat layer coated on the primer layer. The topcoat layer may be mainly composed of (a) 100 parts by weight of a polycarbonate polyurethane resin having a number-average molecular weight of 8,000 or more and a 100% modulus of 20 kg / cm2 or more, and (b) 0.1-40 parts by weight of a (meth)acrylate-butadiene-styrene resin. The surface of the topcoat layer may be subjected to embossing.

Description

The present invention relates to a thermoplastic skin sheet used for interior parts of automobiles, more particularly to a thermoplastic skin sheet suffering from no cracking and rupture by thermal forming, and to a thermoplastic skin sheet with a matte surface suitable for decorative skin sheets for interior parts of automobiles, and their production method.Interior parts of automobiles such as instrument panels should not only be integrally formed into complicated shapes but also have good hand such as softness, elasticity, etc., with matte surfaces such as embossed surfaces. For this purpose, a foamed layer is conventionally disposed between a substrate sheet and a surface skin layer for interior parts of automobiles such as instrument panels, and a surface of the skin layer is subjected to embossing or matte coating.Conventional interior parts have skin sheets made of polyvinyl chloride resins from the aspect of hand, wear resistance, weathering resistance, etc., and inner foam ...

AI Technical Summary

Benefits of technology

Accordingly, a first object of the present invention is to provide a thermoplastic skin sheet capable of being thermally stretch-formed substantially without causing cracking and rupture, thus being suitable for interior parts of automobiles which are formed at high stretching ratio.

The thermoplastic polyolefin resin or the thermoplastic elastomer is melt-blended and formed into a sheet by extrusion or calendaring. Prior to coating a primer, the thermoplastic sheet is preferably heat-treated or irradiated with ultraviolet rays for cross-lining. Cross-linking imparts good heat resistance, durability, wear resistance, etc. to the thermoplastic sheet without losing softness.

Problems solved by technology

However, it is not easy to conduct the separation of polyvinyl chloride resin skin layers from the substrate sheets made of ABS resins or polypropylene, which are bonded to each other via polyurethane foam layers.

In addition, cross-linked, foamed polyurethane layers cannot be recycled.

Further, because environmentally toxic gas is generated by burning the polyvinyl chloride resins, the polyvinyl chloride resins should be burned in large-scale incinerators equipped with toxic gas-removing means.

However, because the skin layers of the interior parts made of a polyolefin resins are poor in coatability, the skin layers should be coated with primers or subjected to corona discharge treatment.

However, any of the above conventional skin sheets are disadvantageous in that they suffer from cracking and rupture on the surface when thermally formed into desired shapes.

Further, the use of chlorinated polyolefin resins such as chlorinated polypropylene as primers in Japanese Patent Laid-Open No. 60-197741 and Japanese Patent Publication No. 7-14655 not only deteriorates the resistance of the skin sheets to hydrocarbon solvents such as petroleum benzene, gasoline, etc., but also causes remarkable thermal discoloration of the skin sheets over a long period of use.

In addition, reactive primers containing saturated polyesters and polyisocyanates disclosed in Japanese Patent Laid-Open No. 60-197741 and Japanese Patent 2,533,147 cause problems that a surface of a thermoplastic skin sheet should be subjected to an oxidation treatment such as a corona discharge treatment, etc., making the entire process too lengthy; and that a mixture of a polyester and a polyisocyanate cannot be stored for a long period of time due to its reactivity, making impossible its reuse later and thus making it inevitable to discard all remaining primer liquids.

(1) With respect to solvent resistance, the chlorinated polypropylene per se is easily eroded by hydrocarbon solvents.

(2) With respect to thermal discoloration, chlorine gas or hydrochloride gas generated by thermal decomposition of the chlorinated polypropylene causes the thermal discoloration.

(3) The reason why the corona discharge treatment is necessary in using reactive primers containing saturated polyesters and polyisocyanates is that the primers would not adhere to surfaces of thermoplastic sheets made of thermoplastic polyolefin resins or thermoplastic elastomers unless polar groups such as hydroxyl group reactive to isocyanate components in the primers are generated.

(4) The reason why the remaining primer liquids cannot be stored for a long period of time is that isocyanate components in the primers containing saturated polyesters and polyisocyanates react with the remaining hydroxyl groups in the saturated polyesters and moisture in the air with time, whereby the isocyanate components become unreactive to polar groups on the surfaces of thermoplastic sheets made of thermoplastic polyolefin resins or thermoplastic elastomers.